1. Field of the Invention
This invention relates to a motor actuated buzzer for an alarm device or a burglar alarm.
2. Prior Art
One conventional buzzer comprises an electromagnet adapted to be excited by either a DC current or an AC current, a sound generating plate, an oscillatory plate carrying a hammer and attracted by the electromagnet to move toward the sound generating plate to bring the hammer into striking contact with the sound generating plate, and a switching means having a first contact mounted on the oscillatory plate and a second contact mounted on a buzzer body, the first contact being moved away from the second contact when the oscillatory plate is moved toward the sound generating plate to de-energize the electromagnet. With this conventional buzzer, the spacing between the first and second contacts as well as the spacing between the oscillatory plate and the electromagnet need to be accurately predetermined so that the oscillatory plate can be operated properly to produce a buzzing sound of a desired volume.
The conventional buzzer has the following disadvantages:
(a) When the buzzer is used over a long period of time, the oscillatory plate, the electromagnet and the sound generating plate become displaced with respect to one another since the buzzer is subjected to vibration during the operation, so that the spacing between the electromagnet and the oscillatory plate as well as the spacing between the first and second contacts is changed. As a result, the volume of the buzzing sound produced may be varied, and in the worst case the oscillatory plate fails to produce a buzzing sound,
(b) A delicate adjustment is required in assembling the buzzer so that the above-mentioned component parts are accurately positioned with respect to one another.
(c) When the buzzer is used in those places, such as a factory and a plant, where a power voltage for the buzzer is subjected to a fluctuation, the oscillatory movement of the oscillatory plate tends to becomes unstable or to be stopped.
(d) When the oscillatory plate is used for a long period of time, it is subjected to fatigue and may finally be subjected to damage or breakage.